Compounds having retinoid-like activity are well known in the art, and are described in numerous United States and other patents and in scientific publications. It is generally known and accepted in the art that retinoid-like activity is useful for treating animals of the mammalian species, including humans, to cure or alleviate the symptoms and conditions of numerous diseases and conditions. Thus, pharmaceutical compositions having a retinoid-like compound or compounds as the active ingredient are useful as treatments and/or cures of a variety of disorders. Retinoid compounds are also useful for preventing and treating cancerous and precancerous conditions, including, premalignant and malignant hyperproliferative diseases such as cancers of the breast, skin, prostate, cervix, uterus, colon, bladder, esophagus, stomach, lung, larynx, oral cavity, blood and lymphatic system, metaplasias, dysplasias, neoplasias, leukoplakias and papillomas of the mucous membranes and in the treatment of Kaposi's sarcoma, modulation of apoptosis, including both the induction of apoptosis and inhibition of T-Cell activated apoptosis and metabolic disorders, such as type 2 diabetes, hyperlipidemia and atherosclerosis.
It is also general knowledge in the art that two main types of retinoid receptors exist in mammals (and other organisms). The two main types or families of receptors respectively designated the Retinoic Acid Receptors (RAR) and Retinoid X Receptors (RXR). Within each type there are subtypes; in the RAR family the subtypes are designated RAR.alpha., RAR.beta. and RAR.gamma., in RXR the subtypes are: RXR.alpha., RXR.beta. and RXR.gamma.
RXRs belonging to the nuclear receptor superfamily consist of a large number of ligand-regulated transcription factors that mediate the diverse physiological functions of steroid hormones, retinoids, thyroid hormone, and vitamin D in embryonic development, growth, differentiation, apoptosis, and homeostasis (Kastner, P., et al., Cell 83, 859-869 (1995); Mangelsdorf, D. J., et al., Cell 83, 841-850 (1995)). The superfamily also includes many orphan receptors whose ligands remain to be identified. All nuclear receptors consist of three domains: the N-terminal domain with varying length, the well conserved DNA binding domain (DBD) and the ligand binding domain (LBD) (Kastner, P., et al., Cell 83, 859-869 (1995); Mangelsdorf, D. J., et al., Cell 83, 841-850 (1995); Heyman, R. A., et al. Cell 68, 397-406 (1992).; Levin et al., Nature 355, 359-361 (1992)). The LBD is responsible for receptor dimerization and its interaction with transcriptional coactivators or corepressors. RXRs mediate retinoid signaling through the RXR/RAR heterodimer and the RXR/RXR homodimers (Kastner, P., et al., Cell 83, 859-869 (1995); Mangelsdorf, D. J., et al., Cell 83, 841-850 (1995); Zhang, X. K., et al., Nature 358, 587-591 (1992b)). In addition, RXRs form heterodimers with many members of the subfamily 1 nuclear receptors, including vitamin D receptor (VDR), peroxisome proliferator-activated receptor (PPAR), and thyroid hormone receptor (TR), as well as several orphan receptors, such as liver X receptor (LXR), pregnane X receptor (PXR), constitutively activated receptor (CAR), and TR3/Nur77/NGFI-B (Kastner, P., et al., Cell 83, 859-869 (1995); Mangelsdorf, D. J., et al., Cell 83, 841-850 (1995)). RXRs, therefore, play an essential role in the regulation of multiple nuclear hormone signaling pathways through their unique and potent heterodimerization capacity.
The role of RXR in regulating transcriptional activation of its heterodimerization partners has been extensively studied (Kastner, P., et al., Cell 83, 859-869 (1995); Mangelsdorf, D. J., et al., Cell 83, 841-850 (1995); Zhang, X. K., et al., Nature 358, 587-591 (1992b)). RXR homodimerization and its heterodimerization are required for efficient DNA binding and transactivation. In the absence of ligands, some nuclear receptors repress transcription of target genes through their interaction with transcriptional corepressors. Ligand binding causes a conformational change of receptors, allowing dissociation of transcriptional corepressors and association of transcriptional coactivators (Xu, L., et al., Curr Opin Genet Dev 9, 140-147 (1999)). However, whether RXR acts nongenotropically to regulate important biological processes remains unknown.
Orphan receptor TR3 (also known as nur77 and NGFI-B) (Chang, C., et al. J Steroid Biochem 34, 391-395 (1989); Hazel, T. G., et al. Natl Acad Sci USA 85, 8444-8448 (1988); Milbrandt, J Neuron 1, 183-188 (1988)) is an immediate-early response gene whose expression is rapidly induced by a variety of extracellular stimuli, including growth factors, phorbol ester and cAMP-dependent pathways. TR3 and its closely related family members, Not-1 (also called Nurr1 and RNR-1) (Law et al., 1992; Mages et al., 1994) and NOR-1 (also called MINOR and TEC) (Hedvat, C. V., et al., Mol Endocrinol 9, 1692-1700 (1995); Ohkura, N., et al., Biochem Biophys Res Commun 205, 1959-1965 (1994)) constitute a distinct subfamily within the nuclear receptor superfamily (Kastner, P., et al., Cell 83, 859-869 (1995); Mangelsdorf, D. J., et al., Cell 83, 841-850 (1995); Zhang, X. K., et al., Nature 358, 587-591 (1992b)). TR3 was originally recognized for its role in cell proliferation and differentiation. Paradoxically, TR3 was later found to be a potent pro-apoptotic molecule (Maruyama, K., et al., Cancer Lett 96, 117-122 (1995)).
TR3 functions in the nucleus as a transcription factor to regulate gene expression necessary to alter the cellular phenotype in response to various stimuli. TR3 response elements (NBRE or NurRE) have been identified (Philips, A., et al., Mol Cell Biol 17, 5946-5951 (1997); Wilson, T. E., et al., Science 252, 1296-1300 (1991)). In addition, it has been shown that TR3 can form a heterodimer with RXR (Forman, B. M., et al. Cell 81, 541-550 (1995); Perlmann and Jansson, Genes Dev 9, 769-782 (1995)), and that TR3 can interact with orphan receptor COUP-TF (Wu et al., Embo J 16, 1656-1669 (1997b)), which binds to the RAR.beta. promoter and is required for efficient RAR.beta. expression (Lin et al., Mol Cell Biol 20, 957-970 (2000)). Through its interaction with RXR and COUP-TF, TR3 modulates RAR.beta. expression and alters the growth response of cells to retinoids (Wu et al., Embo J 16, 1656-1669 (1997b)).
One well-established apoptotic pathway involves mitochondria (Green and Reed, Science 281: 1309-1312 (1998); Green and Kroemer, Trends Cell Biol 8, 267-271(1998)). Cytochrome c is exclusively present in mitochondria and is released from mitochondria in response to a variety of apoptotic stimuli. Expression of TR3 is rapidly induced during apoptosis of immature thymocytes and T-cell hybridomas as well as various types of cancer cells (Li, H., et al. Science 289, 1159-1164 (2000); Li, H., et al., Mol Cell Biol 18, 4719-4731 (1998); Liu, Z. G., et al., Nature 367, 281-284 (1994); Uemura, H., and Chang, C. Endocrinology 139, 2329-2334 (1998); Woronicz, J. D., et al., Nature 367, 277-281 (1994)). Overexpression of a dominant-negative TR3 protein or inhibition of TR3 expression by antisense TR3 inhibited apoptosis, whereas constitutive expression of TR3 results in massive apoptosis (Li, H., et al. Science 289, 1159-1164 (2000); Li, H., et al., Mol Cell Biol 18, 4719-4731 (1998); Liu, Z. G., et al., Nature 367, 281-284 (1994); Uemura, H., and Chang, C. Endocrinology 139, 2329-2334 (1998); Weih et al., 1996; Woronicz, J. D., et al., Nature 367, 277-281 (1994); Woronicz et al., 1995). Recent studies have demonstrated that TR3 acts outside the nucleus to mediate several important biological functions, including apoptosis and differentiation. TR3 translocates from the nucleus to the cytoplasm in response to NGF treatment of PC 12 phaeochromocytoma cells, thus facilitating NGF-induced PC12 cell differentiation. TR3, in response to apoptotic stimuli, translocates from the nucleus to the cytoplasm where it targets mitochondria to induce cytochrome c release (Li, H., et al. Science 289, 1159-1164 (2000)). Induction of cytochrome c release is mediated by a direct interaction of TR3 with Bcl-2, which converts Bcl-2 from a protector to a killer (Li et al., Cell 116, 527-540 (2004)). Thus, in addition to its action in the nucleus, TR3 plays a diverse biological role in the cytoplasm.
Accordingly there is a need for the establishment of new RXR pathways in order to discover and develop therapeutic agents that can act on the RXR mediated pathways.